Magento Custom Maintenance Page (503 Error Page)
Magento is an eCommerce platform, I've set-up Magento for friends and family in the past. It is possible to create a custom maintenance page to match your brand. Instructions on how to do are available here.
However, I couldn't get this to work, Magento kept displaying the default error page. After identifying that the processor.php file was responsible for figuring out what to display, I examined the file and used echo statements to figure out why it was not loading it. In my case this was because the site was running under a hosting account with multiple other websites.
Specifically if you are running multiple websites under a single hosting account and the site with Magento installed is not the primary site - then you need to take some additional steps.
For example with Go Daddy if you keep files for your additional sites in a folder called _sites and have a separate folder for each website, the additional steps you need to modify the processor.php file under the errors folder at the base of your Magento installation. Change line 281 in function protected function _getIndexDir() from:
return dirname($documentRoot . $this->_scriptName) . '/';
return dirname($documentRoot . ‘/_sites/example.com/’ . $this->_scriptName) . '/';